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Poly over Zinsser amber Shellac?

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Forum topic by danr posted 06-26-2012 02:55 AM 8367 views 0 times favorited 17 replies Add to Favorites Watch
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danr

151 posts in 1842 days


06-26-2012 02:55 AM

Topic tags/keywords: question finishing

Hello lumberjocks,

I was just reading the Zinsser shellac data sheet and it states:

“We do not recommend poly over the shellac” It also says that polly is ok over the Zinsser sanding sealer product.

I did a little sample (Minwax poly over Zinsser amber shellac) and it seems to look and feel fine to me. Would any of you finishing folks have any idea why the data sheet might say this or what the potential problems might be? One thought that I had was that maybe the Zinsser shellac product is waxed as opposed to de-waxed. I could not really tell from the Zinsser data sheet.

By the way, I would be spraying the poly.

I would really appreciate it if you have any experience or knowledge in this area and would be willing to share it with me.

Thanks


17 replies so far

View Tedster's profile

Tedster

2271 posts in 868 days


#1 posted 06-26-2012 03:56 AM

In many old houses I work in, poly had been applied over the old oil varnish and had since alligatored. What happens is the oil varnish is slightly viscous but the poly is not, so the poly cracks and floats around like sheets of ice on water. I don’t know about shellac but that may be the same situation—it may look good now but it might eventually alligator.

-- I support the 28th Amendment. http://www.wolf-pac.com/28th

View Fred Hargis's profile

Fred Hargis

1794 posts in 1151 days


#2 posted 06-26-2012 11:02 AM

It’s the wax that may cause the problem. The only Zinsser product that’s de-waxed is the Seal Coat (I think). You can get around this: use a non-poly varnish. It will stick to the amber just fine and (IMHO) give you a better look. brands could be P&L 38, the Cabot 8000 series (8000, 8001, etc.), Sherwin Williams Fast Dry Oil Varnish, and I think Old Masters has a non-poly formula though I’ve never been able to find it. It may look and feel fine now, but over time there is a chance the poly will peel off the shellac.

-- Our village hasn't lost it's idiot, we sent 'em to Washington.

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danr

151 posts in 1842 days


#3 posted 06-26-2012 01:21 PM

Ted and Fred,

Thanks for the reply. I was thinking that one option might be to go ahead and spray a coat of the Zinsser seal coat over the shellac. The seal coat data sheet states that it will stick to anything and anything will stick to it. It is actually promoted as a “binder coat” product “used for bonding two dis-similar coatings.

You had mentioned non-poly varnish. I don’t have any experience with varnishes of any kind. I am trying to find a finishing solution for end-table tops. I was wanting to put something over the shellac on the tops so I would have a bit better protection from water stains from drinking cups/glasses. I thought poly would be a good option to give better protection than the shellac. I have used a lot of shellac but not on pieces that people will be setting glasses on.

Can you give me any feedback on the “protection” qualities of varnish (the non-poly type in particular). Would this be a good option to use for the above stated purpose of giving the better protection against water stains/cup rings?

I really appreciate your feedback. A finishing expert, I am not.

Thanks,

View Cato's profile

Cato

641 posts in 1970 days


#4 posted 06-26-2012 01:34 PM

You could just use a dewaxed amber shellac mixed from flakes and then apply poly over it.

View Bill White's profile

Bill White

3457 posts in 2618 days


#5 posted 06-26-2012 01:49 PM

Put a coat of Seal Coat over the amber shellac (the amber has wax). Then coat with the poly. Although I don’t particularly like poly, it has a place in WWing. Table tops will probably need the added toughness that poly provides.
I often use the Old Masters wiping varnish for areas that don’t need the urethane.
Old Masters also has a wiping poly gel that works well for smaller projects.
Bill

-- bill@magraphics.us

View Fred Hargis's profile

Fred Hargis

1794 posts in 1151 days


#6 posted 06-26-2012 01:55 PM

Danr, in most circles “poly” is varnish, it’s made from polyurethane resins (there are other finishes referred to as “poly” from time to time, mostly water born). The difference between the “poly” and non-poly is the base resins used, and sometimes the oil they are cooked in. The P&L and cabot are alkyd resin/soya oil formulas, the S&W is an alkyd resin/linseed oil formula. There is also Waterlox Original, a phelonic resin formula (not sure which oil they use). Linseed oil formulas are normally what the pol varnishes use, and that is why they have that decidedly amber cast to them. SW fast dry is that way. But open a can of P&L (soya oil) and it looks a purplish-gray in the can, the Cabot is a goldish (I guess) hue. So if you have used what most folks call “poly”, you have indeed used varnish. Also, putting seal coat on top of the amber might still have a risk. Shellac tends to melt into itself (the alcohol in the new coat dissolves whats already there) so so of the wax can come to the surface. I won’t claim the non-poly varnishes are better than poly…it’s chief attribute if scratch resistance. But the other varnishes are just as good (my opinion) as poly on any furniture projects. Poly is great for floor finishes. For water and stains I also think the non-poly is just as good, and may be better than poly. I’m sure sure what exactly you are putting the varnish on, but unless it’s the floor I think the others will be just as good. BTW, it’s actually the urethane resins that cause an adhesion problem with the waxy shellac, that’s why the others will still work.

-- Our village hasn't lost it's idiot, we sent 'em to Washington.

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danr

151 posts in 1842 days


#7 posted 06-26-2012 03:50 PM

Fred,

I think you have convinced me to go with the non-poly varnish over the waxed shellac. Of course I will experiement before applying it to the end tables that I am finishing.

At this point I am only planning to put the varnish on the tops because:
1.) I am very happy iwth the shellac finish results on the rest of the end table.
2.) I am only concerned about protecting the tops from cup/glass water marks.

I also am planning to apply some tinted wax as the final “top-coat” so I am thinking that any slight difference in “color” between the end tabel tops and the rest of the table will be cancelled out by the wax.

I really appreciate your feedback. How did you happen to gain all of this finishing knowledge?

View Fred Hargis's profile

Fred Hargis

1794 posts in 1151 days


#8 posted 06-26-2012 04:35 PM

dnar, I’ve been bouncing around several woodworking forums since about 1999, and picked up some really great advice from some of the experts I’ve “met” over the years. But by far the best thing is to get one (or both ) of 2 books and read them. “Flexnor’s “Understanding Wood Finishing””:http://www.amazon.com/Understanding-Wood-Finishing-American-Woodworker/dp/0762101911/ref=sr11?ie=UTF8&qid=1340728146&sr=8-1&keywords=bob+Flexnor and “Jewitt’s “Illustrated Guide….””:http://www.amazon.com/Tauntons-Complete-Illustrated-Guide-Finishing/dp/1561585920/ref=sr13?s=books&ie=UTF8&qid=1340728312&sr=1-3&keywords=Jeff+Jewitt are just too good for any woodworker to not have them. Flexnor’s book is a little easier to read…I went through it much like a novel. Jewitt’s book is great as a resource to pull out when you have a question. The both contain petty much the same info. Good luck with your project!

-- Our village hasn't lost it's idiot, we sent 'em to Washington.

View Bill White's profile

Bill White

3457 posts in 2618 days


#9 posted 06-26-2012 05:10 PM

“How did you happen to gain all of this finishing knowledge?”
I’ve screwed up enough stuff, fixed enough stuff, and thrown enough stuff away to qualify as a feller that has learned the hard way. I applaud your willingness to ask and learn from others.
The way finishes are changing in today’s market, the learning will continue.
Bill

-- bill@magraphics.us

View pintodeluxe's profile

pintodeluxe

3365 posts in 1471 days


#10 posted 06-26-2012 05:13 PM

I did a wainscoting project in cherry and sealed with dewaxed shellac. Then stain. Then topcoated with pre-cat lacquer. I ran out of space in the shop, so I moved the boards outside when they were dry. After sitting in direct sunlight (75 degree day) the lacquer crinkled. Lacquer only would not have reacted that way.
Ever since then I do not consider dewaxed shellac “universal.”
In fact I like to stick with pre-cat lacquer for all interior projects.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View danr's profile

danr

151 posts in 1842 days


#11 posted 06-26-2012 06:06 PM

Thanks for all the feedback.

I have no experience with lacquer. I just aquired my spray system and used it to spray the shellac. The results were excellent. Now that I have the spray setup, I will consider using lacquer on future projects.

View Fred Hargis's profile

Fred Hargis

1794 posts in 1151 days


#12 posted 06-26-2012 06:22 PM

I have no idea how I screwed up those links…too late now to fix them. Let me try again:
Flexner

Jewitt

Damn, I wish there was a longer edit window.

-- Our village hasn't lost it's idiot, we sent 'em to Washington.

View Milo's profile

Milo

851 posts in 1976 days


#13 posted 06-27-2012 12:47 PM

I always sprayed or padded Water based finish over shellac with excellent results. You may think about that.

-- Beer, Beer, Thank God for Beer. It's my way of keeping my mind fresh and clear...

View danr's profile

danr

151 posts in 1842 days


#14 posted 06-27-2012 03:32 PM

Frrom Fred’s previous response on the descriptions of the ingredients of the various non-poly varnishes.

I aquired some waterlox original (satin) and it is tung oil based. I will be doing some experiments with it over the waxed shellac. waterlox has a nice description on there web-site about how to test the adhesion of finishing products (i.e. the cross-hatch test).

For whatever reason, I am not ready to try any water based products or lacquor yet (fear of the unknown for me). I will be giving these products a try in the future though.

Thanks for all of the feedback

View me5269's profile

me5269

43 posts in 825 days


#15 posted 06-28-2012 11:02 AM

danr,
I use zinsser shellac or waterlox probably 90% of the time. I applied waterlox original over zinsser clear shellac totally by accident, forgot I was using shellac (2 coats applied) and grabbed the waterlox. After a few choice words, and a couple days, it looked ok, so applied another coat of the waterlox.
I like the way it came out and have tried it on a couple more projects (not by mistake these times) with good results.
Note, these were scrollsaw projects, not furniture. I find the shellac (thinned 50-50) will get into the small cutouts easier than the waterlox.

-- Mike

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